Also Known As – BHV-4 – Passenger Virus – Moyar Virus
Introduction
BHV-4 is a member of the Herpesvirus causing reproductive disease in cattle in the form of endometritis, vulvovaginits, associated abortion and mastitis. Most disease is however, subclinical, hence its common name of “passenger virus”.
The virus replicates within mucosal cells and then invades the mononuclear cells, causing generalised infection and crossing the placenta to infect the unborn foetus.
Distribution
Worldwide, although prevalence varies.
BHV-4 is transmitted directly and indirectly via infected materials containing mainly respiratory but also genital secretions from infected animals.
Signalment
A range of ruminants can be infected, including American bison, buffalo, sheep and goats.
The virus has also been isolated from lions and cats.
Clinical Signs
BHV-4 can cause abortion and births of weak or dead lambs, calves and kids. It can also increase the incidence of retained foetal membranes.
In dairy cattle, BHV-4 can cause mastitis and associated udder lesions and milk changes.
The virus has also been isolated from cases of conjunctivitis and respiratory disease but it is unclear and somewhat doubtful whether it was the responsible pathogen in these cases, or an opportunistic invader. The respiratory route is however the main route of transmission of the virus.
As with all herpesviruses, BHV-4 can undergo latency, often residing in the trigeminal ganglia similarly to BHV-1 (IBR) and recrudescing with stress and/or immunosuppression. Recovered cattle often become latent carriers. Both acute and latent infections are highly prevalent in endemic BHV-4 areas.
Diagnosis
BHV-4 can be isolated from nasal or vaginal secretions or from triturated organs harvested from cows at necropsy.
Viral DNA can be detected by PCR.
Anitbodies to BHV-4 can be detected using ELISA and Indirect Immunofluorescence. Immunoperoxidase assays are also available.
It must always be considered that presence and positive identification of BHV-4 does not mean that it is responsible for the observed disease.
Treatment
No treatment except supportive care is available. Recovered animals are often latent carriers of infection and will shed virus sporadically, providing a source of infection for others.
Control
Exclusive use of hygienic measures can gain control of BHV-4. Seropositive animals should be removed wherever possible due to the high likelihood that they are latent carriers of disease. Infected cows that calve should be isolated approaching and following parturition, as huge quantities of virus are shed in uterine exudates.
Vaccines were developed in the USA but are not widely used.
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References
Animal Health & Production Compendium, Bovine Herpesvirus 4 datasheet, accessed 29/07/2011 @ http://www.cabi.org/ahpc/
Animal Health & Production Compendium, Bovine Herpesvirus 4 Infection datasheet, accessed 29/07/2011 @ http://www.cabi.org/ahpc/